Researchers have described and named a new species of hominid in South Africa that lived nearly two million years ago, during a still mysterious period spanning the emergence of modern human beings.

Palaeoanthropologist Lee Berger of the University of the Witwatersrand in Johannesburg calls the discovery unexpected and incredible. He says it has huge implications for the study of the origins of modern humans.

"Many of the bones like the pelvis of the female were found so recently that they are not in this article. Those ladies and gentlemen are potentially a Rosetta stone into the past," Berger said.

An international team of 60 scientists led by Berger have found two skeletons of the new species, which has been named Australopithecus Sediba or or Southern Ape Man. Berger says the name is significant for two reasons.

"Sediba means wellspring or well or natural spring or fountain in Sotho. And we think it very appropriate because not only are they buried within an underground well, but we think a great source of information and knowledge about our ancestry will spring from these skeletons," Berger said.

Sediba had arms as long as those of the orangutan, with short powerful hands that indicate a human-like movement. Berger says it had a pelvis very similar to that of modern humans. "And we think it makes, probably, the best ancestor yet found for early members of the genus homo. We have proposed that it may possibly even be a very good candidate for a direct ancestor of homo erectus; although we are cautious at this time," he said.

Berger says the remains are in a pristine condition and that while about 40 percent of each skeleton has been discovered, a steady flow of new finds makes him hopeful that they will be close to complete by the time they are fully excavated. Berger says a full upper limb has already been discovered.

"And when I mean complete, I mean from the area of the scapula -- the most fragile bone in the body, paper-thin -- complete through the clavicle, down the arm. The first complete humerus ever discovered in the early hominid record, to the first complete radius, to the first complete ulna. And what you can't see in this image, has come out more recently, is a complete hand," Berger said.

The first fossils were discovered by Berger's 9-year-old son, Matthew, in an area known as the Cradle of Human Kind -- not far from where other notable fossils have been found. No excavating has taken place yet. All the fossilized bones have been found in the remains of an ancient cave that likely was about 30 to 50 meters underground some 1.9 million years ago -- the age of the skeletons.

Berger says the two died at the same time or within weeks of each other and would have known each other. Two papers related to the find, by Berger and Paul Dirks, the former head of the University of the Witwatersrand's School of Geosciences, will be published in the journal Science on Friday.